Severity of “Stem rot” in a genetic collection of nursery seedlings of Gmelina arborea Roxb.

Abstract

The objective of this research was to determine the level of susceptibility of nine genotypes of Gmelina arborea Roxb to the appearance of the disease called here “Stem rot.” A diagrammatic scale was developed to measure the severity of the attack of the pathogen on vegetatively propagated seedlings. For this purpose, four thousand plants were checked and monitored for the first symptoms of the disease to understand the development of the pathology. The scale was applied to 100 plants of each of the nine clones produced to validate it. Statistical analysis was then used to determine the differences between genotypes. The first signs of the disease are spots, stretch marks, and/or small necrotic areas usually at the base of the stem. These evolve until the stem rots, compromises its rigidity, breaks, and the plant dies. Based on this, the proposed diagrammatic scale consists of four degrees of severity of the damage, i.e., starts from "0", a plant free of visible symptoms, and culminates in "3", which is when the stem has rotted and the plant died. Statistical analyses suggest a genetic effect in terms of the susceptibility of the manifestation of the pathology, by identifying clones 16 and 8, and 15 and 1, as those with low and high susceptibility to the disease, respectively. Despite registering relatively low incidence and severity values, actions must be taken to prevent its occurrence, or otherwise, control it.